Method for sizing paper

ABSTRACT

Internal sizing of paper and paper products by the method involving addition to the pulp slurry of a fatty acid sizing agent, such as the sodium salt of stearic acid, and precipitation of the sizing agent onto the pulp fibers with a water-soluble polyvalent metal salt, such as alum or aluminum chloride, is improved by incorporating in the slurry a water-soluble polyfunctional carboxylic acid salt. A substantial increase in the resistance of the paper or paper product to penetration by water or aqueous solutions is achieved as a result of the action of the polyfunctional carboxylic acid salt.

United States Patent [72] Inventors [54] METHOD FOR SIZING PAPER 22 Claims, No Drawings [52] US. Cl 106/243, 162/158, 162/179 [51] Int. CL. C08h 9/00 [50] Field of Search 106/243; 162/178,179, 158; 117/167 [56] References Cited UNITED STATES PATENTS 1,809,470 6/1931 Budowski 106/243 3,008,868 11/1961 Feigley 3,207,603 9/1965 Savit Primary Examiner-Morris Liebman Assistant Examiner-T. Morris AttorneysWalter O. l-lodsdon and Alfred P. Lorenzo chloride, is improved by incorporating in the slurry a water-' soluble polyfunctional carboxylic acid salt. A substantial increase in the resistance of the paper or paper product to penetration by water or aqueous solutions is achieved as a result of the action of the polyfunctional carboxylic acid salt.

This invention relates in general to the manufacture of paper and paper products, such as paperboard. More particularly, this invention relates to an improved method for sizing paper which serves to impart greatly increased resistance to penetration by water or aqueous solutions, to novel sizing compositions utilized in practicing this method, and to the sized paper or paper product produced therewith.

Sizing of paper is a very old and well established art and a wide variety of materials have been proposed heretofore for this purpose. As is well known, the sizing agent may be applied to the fibers during the paper-making operation, in which case the process is called internal sizing (also known as beater sizing or engine sizing), or it may be applied to the surface of the paper after web formation, in which case it is called external or surface sizing. A particularly important class of sizing agents for internal sizing are the fatty acid sizing agents, i.e., sodium, potassium or ammonium salts of long chain saturated fatty acids. In employing these agents, it is conventional practice to add the sizing agent to the paper furnish and thereafter add a precipitating agent which aids in setting the size on the paper-making fibers. The precipitating agents used are watersoluble polyvalent metal salts, such as alum or aluminum chloride. Use of the aforesaid combination of sizing agent and precipitating agent can be accomplished in conventional paper-making machines without the aid of any special apparatus. Moreover, the materials used are of low cost and are generally quite effective in imparting to paper the ability to resist penetration by liquids. However, there are certain significant limitations and disadvantages associated with their use. For example, in some instances the water resistance attainable with these agents is inadequate. Furthermore, in using these sizing agents at the concentrations customarily employed serious problems can arise with regard to formation of translucent spots in the paper and there may also be problems associated with accumulation of the sizing agent at the press rolls of the paper-making machine or with clogging of pipes or other equipment by the sizing agent.

The method of this invention provides a valuable improvement in the hereinabove described process of internal sizing of paper by application of a fatty acid sizing agent followed by a precipitating agent. In accordance with this improved method, a water-soluble polyfunctional carboxylic acid salt, as hereinafter defined in full detail, is employed in conjunction with the sizing agent and precipitating agent. The polyfunctional carboxylic acid salt functions so as to provide a substantially greater resistance to penetration by water or aqueous solutions for a given level of sizing agent, or to permit the production of paper using a lower lever of sizing agent, with consequent reduction in cost and elimination of problems caused by accumulation of excess size, without any reduction in penetration resistance.

More specifically, this invention is based on the discovery that certain water-soluble salts of polyfunctional carboxylic acids, i.e., carboxylic acids having two or more functional groups, can be utilized in conjunction with fatty acid sizing agents and water-soluble polyvalent metal salt precipitating agents to produce paper and paper products with greatly enhanced resistance to penetration by water or aqueous solutions, including alkaline, neutral, and acidic solutions. Use of the polyfunctional carboxylic acid salts has been found to provide a major increase in penetration resistance, as evidenced by standard tests such as the acid penetration test or carbonate penetration test, without significant detrimental effects on other properties, such as wetand dry-strength.

The improved paper and paper products of this invention are comprised of cellulosic paper-making fibers together with a sizing agent, a precipitating agent, and a polyfunctional carboxylic acid salt, as hereinbefore described; these three agents having interacted and combined with one another and with the fibers in such manner as to enchance the penetration resistance of the paper. The paper or paper product can be made from any conventional type of pulp, such as sulflte, kraft or soda, cooked softwood, hardwood or groundwood, rag, rope, jute, and the like, and the pulp can be either bleached or unbleached. Partially esterified cellulose fibers, such as are described in U.S. Pat. Nos. 3,062,679 and 3,096,231, can be used and the furnish may, if desired, include minor amounts of synthetic organic fibers and/or mineral fibers.

The fatty acid sizing agents utilized in practicing this invention are well known in the paper-making art. They are used in place of the more commonly utilized rosin size where it is necessary that the paper resist penetration by organicsolv'ents as well as penetration by aqueous solutions, an important example of such use being the manufacture of photographic papers. The fatty acid sizing agents known to the art are sodium, potassium or ammonium salts of saturated fatty acids of 12 to 22 carbon atoms, such as lauric acid, tridecyclic acid, myristic acid, pentadecylic acid, palmitic acid, margarie acid, stearic acid, nondecylic acid, arachidic acid, behenic acid, and the like. For the purposes of this invention, the preferred fatty acids are those containing 16 to 18 carbon atoms and it is particularly preferred to employ a salt of stearic acid, especially sodium stearate, as the sizing agent. The fatty acid salt used as the size may be prepared from a single saturated fatty acid, or from a mixture of two or more of such acids, and unsaturated fatty acids may be present in the mixture in minor proportions.

in order to set the fatty acid sizing agent, it is conventional practice in the paper-making an to utilize a water-soluble polyvalent metal salt which reacts with the sizing agent to precipitate it onto the paper-making fibers, apparently in the form of an insoluble complex. Suitable salts for this purpose are those in which the polyvalent metal ion is the aluminum. iron or chromium ion and the anion moiety is derived from a strong mineral acid, for example, the sulfate, nitrate, or chloride ion. lllustrative examples of such salts are aluminum chloride, aluminum sulfate, aluminum nitrate, ferric sulfate and chromic sulfate. It is preferred to employ aluminum salts in the practice of this invention. Aluminum sulfate and potassium sulfate-aluminum sulfate salts are ordinarily referred to as alums; the term anhydrous alum" referring to A l,(SO.) the term papermakers alum" referring to Al (SO,) -18H,0, and the term common alum referring to KAl(S0,) -1 211,0. For the purposes of this invention, preferred precipitating agents are aluminum chloride (A1Cl and papermakers alum.

For further details of the process of internal sizing of paper with a fatty acidsizing agent and a water-soluble polyvalent metal salt precipitating agent, reference may be made to U.S. Pat. No. 1,840,399 and 3,096,231.

As hereinbefore indicated, conventional practice with respect to internal sizing of paper with a combination of a fatty acid sizing agent and a water-soluble polyvalent metal salt precipitating agent is modified in accordance with this invention by the additional utilization of a polyfunctional carboxylic acid salt in an amount sufficient to improve the resistance of the paper or paper product to penetration by aqueous solutions. For the purposes of this invention, the useful polyfunctional carboxylic acid salts are water-soluble salts of a polyfunctional carboxylic acid selected from the group consisting of oxalic acid, lower alpha-hydroxycarboxylic acids, lower ketonic acids, and polyaminopolyacetic acids. These carboxylic acids are all well known materials, many of which are commercially available.

The term lower alpha-hydroxycarboxylic acid is employed herein to designate a carboxylic acid containing 2 to 12 carbon atoms and comprising at least one carboxyl radical and at least one hydroxyl group with the hydroxyl group being in the alpha position, i.e., attached to a carbon atom which is immediately adjacent to a carboxyl radical. Useful acids of this class include those containing from one up to as many as five carboxyl radicals and from one up to as many as five hydroxyl groups in the molecule. lllustrative examples of the numerous alpha-hydroxycarboxylic acids of utility in this invention are the following:

gluconic acid,

citric acid,

glycolic acid,

lactic acid,

tartaric acid,

malic acid,

saccharic acid,

alpha-hydroxyadipic acid, and the like.

The term lower ketonic acid is employed herein to designate a carboxylic acid of up to 6 carbon atoms containing both a carbonyl group and a carboxyl radical. Illustrative examples of lower ketonic acids of utility in this invention are pyruvic acid, acetoacetic acid, levulinic acid, and the like.

The term polyaminopolyacetic acid is employed herein to designate an acid containing two or more amino groups and two or more acetic acid groups. illustrative examples of the numerous polyaminopolyacetic acids of utility in this invention are the following:

ethylenediamine tetraacetic acid,

diethylenetriamine pentaacetic acid,

ortho-diamine cyclohexane tetraacetic acid,

ethylene glycol bis(aminoethyl ether) tetraacetic acid,

diaminopropanol tetraacetic acid,

N-( 2-hydroxyethyl)ethylenediamine triacetic acid, and the like.

As previously indicated, the polyfunctional carboxylic acid is utilized in this invention in the form of a water-soluble salt. The nature of the cation in such salt is not critical and useful salts include the ammonium salts, alkali metal salts such as the sodium or potassium salts, and alkaline earth metal salts, such as the calcium salts. For incorporation in the pulp slurry, either the polyfunctional carboxylic acid or a water-soluble salt thereof may be used, it being apparent that in the alkaline environment of the pulp slurry the acid will be rapidly converted to the salt form.

In the practice of this invention, the sizing agent, precipitating agent and polyfunctional carboxylic acid salt can be utilized within a broad range of proportions. Thus, the sizing agent may be advantageously employed in a proportion of from about 0.001 to about 0.1 parts of fatty acid salt per part by weight of the paper-making fibers on a dry basis, with the preferred proportion being in the range from about 0.005 to about 0.02 parts per part by weight. Within these ranges the specific amount used will, of course, depend on such factors as the type of pulp employed, the operating conditions of the paper-making process, and the particular end use for which the paper or paper product is intended. The amount of precipitating agent used will typically be in the range from about 0.2 to about 10 parts per part by weight of sizing agent, i.e., about 0.2 to about 10 parts of polyvalent metal salt per part by weight of fatty acid salt, and preferably in the range from about 0.5 to about 2 parts per part by weight. The polyfunctional carboxylic acid salt can be utilized in any penetration resistance improving amount in accordance with this invention. Suitable amounts of the polyfunctional carboxylic acid salt range from about 0.005 to about 1 part per part by weight of sizing agent, i.e., about 0.005 to about 1 part of polyfunctional carboxylic acid salt per part by weight of fatty acid salt, with the preferred amount being in the range of from about 0.01 to about 0.1 parts per part by weight.

In carrying out the method of this invention, the polyfunctional carboxylic acid salt may be added separately to the pulp slurry or its addition may be efiected by combining it with the sizing agent or with the precipitating agent. The consistency of the pulp slurry at the time these agents are added can vary widely, for example, amounts of from about 0.1 to about 5 percent of dry fibers based on the total weight of the slurry are ordinarily suitable. In any instance, vigorous agitation of the pulp slurry during addition is desirable in order to uniformly distribute the materials throughout the slurry. A preferred procedure is to first prepare an aqueous solution or dispersion of the sizing agent and add the polyfunctional carboxylic acid salt thereto, then add this mixture to the pulp slurry, and thereafter add the precipitating agent to the pulp slurry. For optimum results, the polyfunctional carboxylic acid salt should be thoroughly dispersed in the solution of sizing agent so as to form a homogeneous composition. Aqueous compositions comprising a mixture of fatty acid sizing agent and polyfunctional carboxylic acid salt, as hereinbefore defined, are novel compositions useful for internal sizing of paper and paper products in accordance with this preferred method and it is intended to encompass such compositions, as well as their use in manufacture of paper and paper products, within the scope of this invention.

The sizing agent, precipitating agent and polyfunctional carboxylic acid salt utilized in the method of this invention can be incorporated in the furnish at any point prior to sheet formation, for example, in the beater, stock chest, Jordan engine, fan pump or head box. Control of the pH of the furnish can be accomplished in accordance with conventional practice in the art, for example, by regulating the amount of the precipitating agent which is added, or by addition of an acid or base, as required.

While it is essential in the practice of this invention to employ all three of the hereinbefore described materials, i.e., the sizing agent, the precipitating agent and the polyfunctional carboxylic acid salt, other additives commonly used in the paper-making art can also be utilized to advantage in manufacture of the improved paper and paper products of this invention. Thus, for example, it may be desired in particular instances to employ such additives as fillers, e.g., clays or pigments such as titanium dioxide, wet strength resins, e.g., the amino-aldehyde or polyamide epichlorohydrin resins, dry strength agents, e.g., starches, including both ordinary starch and cationic starch, or polyacrylamide resins, and water-soluble gums, e.g. cellulose ethers such as carboxymethyl cellulose.

The paper and paper products of this invention may be utilized to advantage wherever good resistance to penetration by aqueous solutions is needed. Thus, the invention may be utilized in manufacture of wrapping paper, in manufacture of paper to be used for preparation of gummed labels, in manufacture of paper employed to make bags, and in manufacture of paperboard for use in making boxes. An especially important use of the method disclosed herein is its use in the manufacture of photographic papers, in view of the fact that such papers should be highly resistant to penetration by aqueous solutions encountered in photographic processing operations, including both strongly acid and strongly alkaline solutions. For the manufacture of such photographic papers, optimum results are achieved in accordance with this invention by use of sodium stearate as the sizing agent, aluminum chloride as the precipitating agent and sodium gluconate as the polyfunctional carboxylic acid salt, and this combination represents a preferred embodiment of the invention.

The invention is further illustrated by the following examples of its practice. In these examples, amounts of additives based on fiber content of the pulp slurry are in terms of weight percent of the additive based on bone dry fiber weight. The stearic acid used was commercial stearic acid and was thus a mixture of stearic and palmitic acids also containing minor amount of other saturated fatty acids.

EXAMPLE 1 A pulp slurry, identified hereinafter as pulp slurry (a), was prepared by dispersing 57 grams of one hundred percent softwood high-alpha bleached sulfite pulp in L6 liters of water containing 0.5 percent carboxymethyl cellulose and beating to a Jordan slowness of 48 seconds. A sizing solution was prepared by dissolving 14.0 grams of stearic acid and 4.1 grams of sodium hydroxide in 734 milliliters of water. After diluting the aforesaid pulp slurry with 4 liters of water, there was added thereto, slowly and with rapid agitation, 46 milliliters of the aforesaid sizing solution to which 0.03 grams of sodium gluconate had been added. Aluminum chloride solution was then added to the pulp slurry until a test sample showed the pH had been decreased to a value of 4.5 (this required l.7 parts of aluminum chloride per part by weight of sodium stearate) whereupon the slurry was diluted in a proportioner and handsheets were formed in a Williams mold and dried against a hotplate at l l C. The handsheets had a basis weight of 40 lbs/ 1000 ft. To determine the ability of the paper to resist penetration by aqueous solutions, the handsheets were subjected to an acid penetration test in which a sample of the paper is contacted'on both sides with an aqueous solution containing 7.5 grams of sodium chloride and 625 cc. of glacial acetic acid per liter of solution and the time in seconds until the paper will conduct an electric current of 20 milliamperes is measured. The value obtained for the test handsheet was 702 seconds as compared with a value of 86 seconds for a control handsheet prepared in an identical manner except that the sodium gluconate was omitted.

EXAMPLE 2 Handsheets were prepared from pulp slurry (a) in a similar manner to that described in Example 1 except that 0.05 grams of the disodium salt of ethylenediamine tetraacetic acid was substituted for the 0.03 grams of sodium gluconate and the acid penetration value obtained was 395, as compared with 86 for the control test.

EXAMPLE 3 EXAMPLE 4 l-landsheets were prepared from pulp slurry (a) in a similar manner to that described in example 1 except that 0.05 grams of ortho-diamine cyclohexane tetraacetic acid was substituted for the 0.03 grams of sodium gluconate and the acid penetration value obtained was 206, as compared with 86 for the control test.

7 EXAMPLE 5 Handsheets were prepared from pulp slurry (a) in a similar manner to that described in example 1 except that 0.05 grams of ethylene glycol bis(aminoethyl ether) tetraacetic acid was substituted for the 0.03 grams of sodium gluconate and the acid penetration value obtained was 193, as compared with 86 for the control test.

. EXAMPLE 6 A pulp slurry, identified hereinafter as pulp slurry (b), was prepared using the same type of pulp and similar procedures to those of example 1 and a control handsheet prepared therefrom in a similar manner to that described in example 1 was found to have an acid penetration value of 44, as compared with a value of 86 for the control handsheet in example 1. A test handsheet was prepared in a similar manner to that described in example 1 except that potassium oxalate was used in place of sodium gluconate. The potassium oxalate was used in an amount of 0.043 moles per mole of sodium stearate and the acid penetration value obtained was 210.

EXAMPLE 7 Handsheets were prepared from pulp slurry (b) in a similar manner to that described in example 1 except that in place of the sodium gluconate there was added glycolic acid in an amount of 0.043 moles per mole of sodium stearate and the acid penetration value obtained was 191, as compared with 44 for the control test.

6 EXAMPL 8 Handsheets were prepared from pulp slurry (b) in a similar manner to that described in example 1 except that in place of the sodium gluconate there was added levulinic acid in an amount of 0.043 moles per mole of sodium stearate and the acid penetration value obtained was 170, as compared with 44 for the control test.

EXAMPLE 9 Handsheets were prepared from pulp slurry (b) in a similar manner to that described in example I except that in place of the sodium gluconate there was i added lactic acid in an amount of 0.043 moles per mole of sodium stearate and the acid penetration value obtained was 155, as compared with 44 for the control test.

EXAMPLE 10 Using the same type of wood pulp as is described in example 1, a pulp slurry of the same consistency was prepared, except that no carboxymethyl cellulose was employed, and the slurry was beaten in a Valley beater to a slowness of 30 seconds. This pulp slurry is identified hereinafter as pulp slurry (c). In preparing the test handsheet, the amounts of sodium stearate and of sodium gluconate used were the same as in example l. The acid penetration value obtained was 203 seconds as compared with a value of 7 seconds for a control handsheet prepared in an identical manner except that the sodium gluconate was omitted.

EXAMPLE 1 l EXAMPLE 12 l-landsheets were prepared from pulp slurry (d) in a similar manner to that described in example 1 except that 0.045 grams of citric acid was substituted for the 0.03 grams of sodium gluconate and the acid penetration value obtained was 337, as compared with 28 for the control test.

EXAMPLE 13 .To 25 lbs of pulp slurry, identified hereinafter as pulp slurry (e), having a Jordan slowness of 34 seconds, and composed of a blend of kraft and sulfite pulps from both softwoods and hardwoods, there was added 2.5 gallons of water containing 0.41 lbs sodium stearate, 0.06 lbs sodium hydroxide, and 6.2 grams sodium gluconate. Corn starch in an amount of 3 weight percent based on pulp was also added. Aluminum chloride was then added to the slurry, in an amount sufficient to reduce the pH to 4.5, along with 1.7 weight percent of a melamineforrnaldehyde wet strength agent. At this point the pulp slurry had a consistency of 2.7 percent, i.e., it consisted of 2.7 percent by weight of fibersv Paper waszprepared from this slurry on a small experimental paper machine. To determine the ability of the paper to resist penetration by aqueous solutions, the paper sheet was subjected to the acid penetration test described in example 1 and to a carbonate penetration test in which a sample of the paper is contacted on both sides with a 5 percent aqueous solution of sodium carbonate and the time in seconds until the paper will conduct an electric current of 50 milliamperes is measured. The values obtained were 316 seconds for acid penetration and 354 seconds for carbonate penetration as compared with 185 seconds for acid penetration and 278 seconds for carbonate penetration for paper prepared in an identical manner except that the sodium gluconate was omitted.

EXAMPLE 14 To illustrate the effect of varying the proportion of polyfunctional carboxylic acid salt utilized, a series of handsheet tests were conducted in a similar manner to that described in example 1 using pulp slurry (d) and employing the disodium salt of ethylenediamine tetraacetic acid as the polyfunctional carboxylic acid salt. Results obtained were as follows:

To further illustrate the effect of varying the proportion of polyfunctional carboxylic acid salt utilized, a series of handsheet tests were conducted in a similar manner to that described in example I using pulp slurry (d) and employing sodium gluconate as the polyfunctional carboxylic acid salt. Results obtained were as follows:

Grams of sodium gluconate per Acid Carbonate gram of sodium Penetration Penetration Test No. stearate (seconds) Control 37 426 I 0.016 145 464 EXAMPLE 16 A pulp slurry, identified hereinafter as pulp slurry (f), was prepared from one hundred percent softwood high-alpha bleached sulfite pulp. It contained 0.5 weight percent wood fibers, 0.01 parts per part by weight of fibers of a cationic thermosetting polyamide-epichlorohydrin wet-strength resin prepared from diethylene triamine, adipic acid and epichlorohydrin, 0.005 parts per part by weight of fibers of carboxymethyl cellulose, and 0.0l5 parts per part by weight of fibers of cationic starch. A sizing solution was prepared by mixing together stearic acid, sodium hydroxide solution and sodium gluconate solution in a proportion of 9.6 grams stearic acid to 30 cc. of percent sodium hydroxide to 350 cc. of 0.1 percent sodium gluconate. The sizing solution was added to the pulp slurry in a proportion of 1.6 parts of sizing solution per 100 parts by weight of fibers, aluminum chloride solution was then added in a proportion sufficient to reduce the pH to a value of 4.8, and handsheets were prepared from the slurry. The acid penetration value was 236 seconds as compared with 34 seconds for a handsheet prepared in an identical manner except that the sodium gluconate was omitted.

8 EXAMPLE 1? Three mill tests were conducted in which three different stocks were treated with the sizing solution described in example l6 and precipitation was effected by addition of aluminum chloride solution.

In test one, 3,000 lbs of a mixture of softwood and hardwood bleached sulfites (60:40) were used to prepare a slurry containing 2.2 weight percent of wood fibers and having a Jordan slowness of 20 to 25 seconds. To the pulp slurry there was added 1.0 weight percent of a melamine-formaldehyde wet strength agent, 2.0 weight percent of the sizing solution comprising sodium stearate and sodium gluconate described in example 16, 2.0 weight percent of starch, and aluminum chloride in an amount sufiicient to reduce the pH to 4.0. A paper sheet was formed on a conventional Fourdrinier paper machine, dried, tub sized with a 4 weight percent solution of gelatin in water, redried, and calendered.

ln test two, the procedure of test one was followed except that the fiber furnish was percent softwood bleached sulfite, the Jordan slowness was 25 to 30 seconds, the amount of melamine-formaldehyde wet strength agent was 0.3 percent, and the amount of sizing solution was 1.0 percent.

In test three, the paper was prepared in the same manner as in test one and the composition of the pulp slurry was the same as is described in example l6.The slurry contained 3,600 lbs of fiber, and had a consistency of 1.2 percent and a Jordan slowness of 30 to 35 seconds.

For purposes of comparison, control runs were made in which all conditions were substantially the same as in the test run except that no sodium gluconate was employed, and, in each instance, samples of the paper were tested for acid penetration resistance. Results obtained were as follows:

As illustrated by the handsheet, experimental paper machine, and mill test results presented herein, paper prepared in accordance with this invention, i.e. with the aid of a polyfunctional carboxylic acid salt in addition to the prior art use of fatty acid sizing agent and water-soluble polyvalent metal salt precipitating agent, exhibits substantially improved resistance to penetration by aqueous solutions. Moreover, it has been noted that this improvement in penetration resistance is accomplished without any significant detrimental effect on other properties of the paper.

As indicated hereinbefore, several alternative methods of effecting the incorporation of the sizing agent, precipitating agent and polyfunctional carboxylic acid salt in the pulp slurry are feasible. Thus, for example, tests in which sodium stearate was used as the sizing agent, aluminum chloride as the precipitating agent, and sodium gluconate as the polyfunctional carboxylic acid salt were carried out by the following procedures:

a. the sodium gluconate was added to the pulp slurry, then the sodium stearate was added, and then the aluminum chloride was added,

b. a mixture of sodium gluconate and sodium stearate was added to the pulp slurry and then the aluminum chloride was added,

c. the sodium stearate was added to the pulp slurry and then a mixture of sodium gluconate and aluminum chloride was added,

d. the sodium gluconate was added to the pulp slurry. then the aluminum chloride was added, and then the sodium stearate was added.

e. the aluminum chloride was added to the pulp slurry and then a mixture of sodium stearate and sodium gluconate was added,

f. a mixture of sodium gluconate and aluminum chloride was added to the pulp slurry and then the sodium stearate was added. Comparable values for acid penetration resistance were obtained with each of procedures (a) through (f).

The present invention may be utilized advantageously, whenever greater resistance to penetration by aqueous solutions than is attainable by the prior art method is desired, by using the same level of sizing agent and incorporating the polyfunctional carboxylic acid salt in an amount sufficient to enhance the penetration resistance. On the other hand, for those applications in which the degree of penetration resistance provided by the prior art method is adequate, the invention may still be advantageously employed by decreasing the amount of sizing agent utilized in the prior art procedure and utilizing the polyfunctional carboxylic acid salt to achieve the same level of penetration resistance as previously obtained. Reduction in the amount of sizing agent used of as much as about one half is feasible in many instances. Thus, by this means, significant economic savings resulting from the reduced use of sizing agent can be achieved and many of the problems heretofore encountered as a result of the relatively large amounts of sizing agent needed can be eliminated, or at least substantially reduced.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. In a process for internal sizing of paper or paper products in which an aqueous pulp slurry comprising cellulosic papermaking fibers is mixed with a fatty acid sizing agent containing l2-22 carbon atoms and with a water-soluble polyvalent metal salt precipitating agent which acts to precipitate the sizing agent onto the fibers, the improvement comprising mixing with said pulp slurry a polyfunctional carboxylic acid salt in an amount sufficient to improve the resistance of the paper or paper product to penetration by aqueous solutions, said polyfunctional carboxylic acid salt being a water-soluble salt of a carboxylic acid selected from the groupconsisting of oxalic acid, lower alpha-hydroxycarboxylic acids containing 2-12 carbon atoms, lower ketonic acids containing up to 6 carbon atoms, and polyaminopolyacetic acids.

2. The process as described in claim 1 wherein said sizing agent and said polyfunctional carboxylic acid salt are mixed together in an aqueous solution, said solution is added to said pulp slurry, and thereafter said precipitating agent is added to said pulp slurry.

3. The process as described in claim 1 wherein said sizing agent is employed in a proportion of from about 0.001 to about 0.1 parts per part by weight of said fibers, said precipitating agent is employed in a proportion of from about 0.2 to about 10 parts per part by weight of said sizing agent, and said polyfunctional carboxylic acid salt is employed in a proportion of from about 0.005 to about 1 part per part by weight of said sizing agent.

4. The process as described in claim 1 wherein said sizing agent is employed in a proportion of from about 0.005 to about 0.02 parts per part by weight of said fibers, said precipitating agent is employed in a proportion of from about 0.5 to about 2 parts per part by weight of said sizing agent, and said polyfunctional carboxylic acid salt is employed in a proportion of from about 0.01 to about 0.1 parts per part by weight of said sizing agent.

5. The process as described in claim 1 wherein said sizing agent is a salt of a saturated fatty acid of 16 to 18 carbon atoms.

6. The process as described in claim 1 agent is a salt of stearic acid.

7. The process as described in claim 1 agent is sodium stearate.

he process as described In claim 1 whereln said precipitating agent is an aluminum salt.

9. The process as described in claim 1 wherein said precipitating agent is aluminum chloride.

10. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is sodium gluconate.

11. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is sodium citrate.

12. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is potassium oxalate.

13. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is a sodium salt of ethylenediamine tetraacetic acid.

14. The process as described in claim 1 wherein said sizing agent is sodium stearate, said precipitating agent is aluminum chloride, and said polyfunctional carboxylic acid salt is sodium gluconate.

15. Paper or a paper product sized by the process of claim I.

16. Paper or a paper product sized by the process of claim 2.

17. Paper or a paper product sized by the process of claim 4.

18. Paper or a paper product sized by the process of claim l4.

19. An aqueous composition for use in internal sizing of paper and paper products comprising a fatty acid sizing agent containing 12-22 carbon atoms and a water-soluble salt of a carboxylic acid selected from the group consisting of oxalic acid, lower alpha-hydroxycarboxylic acids containing 2-12 carbon atoms, lower ketonic acids containing up to 6 carbon atoms, and polyaminopolyacetic acids.

20. A composition as described in claim 19 wherein said sizing agent is a salt of a saturated fatty acid of 16 to l8 carbon atoms.

21. A composition as described in claim 19 wherein said sizing agent is sodium stearate.

22. A composition as described in claim 19 wherein said sizing agent is sodium stearate and said salt is sodium gluconate.

wherein said sizing wherein said sizing 

2. The process as described in claim 1 wherein said sizing agent and said polyfunctional carboxylic acid salt are mixed together in an aqueous solution, said solution is added to said pulp slurry, and thereafter said precipitating agent is added to said pulP slurry.
 3. The process as described in claim 1 wherein said sizing agent is employed in a proportion of from about 0.001 to about 0.1 parts per part by weight of said fibers, said precipitating agent is employed in a proportion of from about 0.2 to about 10 parts per part by weight of said sizing agent, and said polyfunctional carboxylic acid salt is employed in a proportion of from about 0.005 to about 1 part per part by weight of said sizing agent.
 4. The process as described in claim 1 wherein said sizing agent is employed in a proportion of from about 0.005 to about 0.02 parts per part by weight of said fibers, said precipitating agent is employed in a proportion of from about 0.5 to about 2 parts per part by weight of said sizing agent, and said polyfunctional carboxylic acid salt is employed in a proportion of from about 0.01 to about 0.1 parts per part by weight of said sizing agent.
 5. The process as described in claim 1 wherein said sizing agent is a salt of a saturated fatty acid of 16 to 18 carbon atoms.
 6. The process as described in claim 1 wherein said sizing agent is a salt of stearic acid.
 7. The process as described in claim 1 wherein said sizing agent is sodium stearate.
 8. The process as described in claim 1 wherein said precipitating agent is an aluminum salt.
 9. The process as described in claim 1 wherein said precipitating agent is aluminum chloride.
 10. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is sodium gluconate.
 11. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is sodium citrate.
 12. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is potassium oxalate.
 13. The process as described in claim 1 wherein said polyfunctional carboxylic acid salt is a sodium salt of ethylenediamine tetraacetic acid.
 14. The process as described in claim 1 wherein said sizing agent is sodium stearate, said precipitating agent is aluminum chloride, and said polyfunctional carboxylic acid salt is sodium gluconate.
 15. Paper or a paper product sized by the process of claim
 1. 16. Paper or a paper product sized by the process of claim
 2. 17. Paper or a paper product sized by the process of claim
 4. 18. Paper or a paper product sized by the process of claim
 14. 19. An aqueous composition for use in internal sizing of paper and paper products comprising a fatty acid sizing agent containing 12-22 carbon atoms and a water-soluble salt of a carboxylic acid selected from the group consisting of oxalic acid, lower alpha-hydroxycarboxylic acids containing 2-12 carbon atoms, lower ketonic acids containing up to 6 carbon atoms, and polyaminopolyacetic acids.
 20. A composition as described in claim 19 wherein said sizing agent is a salt of a saturated fatty acid of 16 to 18 carbon atoms.
 21. A composition as described in claim 19 wherein said sizing agent is sodium stearate.
 22. A composition as described in claim 19 wherein said sizing agent is sodium stearate and said salt is sodium gluconate. 